Oxidatively drying water soluble binders based on alkyd resins are known (see e.g. German Patent Specification No. 1 669141 and EP-A-No. 2 488 and the literature cited there). Coatings produced from these binders are normally distinguished by their good optical and mechanical properties as films. One disadvantage of these products, however, is their susceptibility to saponification in aqueous, neutralized solution due to the basic polyester structure. Under storage conditions, the products undergo phase separation and settle out. It would also be desirable to obtain shorter drying times in such alkyd resins.
One alternative to such binders are the polymer binders which dry by purely physical means and which are distinguished by very rapid drying and excellent storage stability (see e.g. DE-OS No. 3 209 421, EP-A-No. 95 263, G. Y. Talak, S. P. Pontis, Paint & Resin 12/83, pages 34 et seq). These products have, however, the disadvantage that the coatings are inferior in their film optical values and have little resistance to solvents due to the lack of chemical cross-linking.
In order to render these systems more resistant to external influences, polyacrylates which dry at room temperature have been modified with oxidatively cross-linkable components, e.g. by the reaction of glycidyl co-polymers with drying fatty acids (e.g. GB-PS Nos. 793 776 and 1 227 398) or by the esterification of OH functional co-polymers with drying fatty acids (e.g. DF-OS No. 2 728 568).
These binders have, however, failed to become established on account of their cost as well as some lacquer technical disadvantages such as slow drying and problems which arise when the lacquer is recoated due to a marked tendency of the recoated lacquer film to lift from the surface. Moreover, such binders are not suitable for use in water dilutable systems.
It was therefore an object of the present invention to provide a binder which would ensure rapid physical drying of coatings combined with good film optical values and which would in addition undergo oxidative cross-linking and be usable in aqueous systems and resistant to saponification and stable in storage and would in addition contain a very low proportion of organic solvent in its aqueous, neutralized form, preferably less than 10%.